[BUG] NiftyReg doesn't deal with spaces in file names

[adamltyson]

As with amap, see https://github.com/SainsburyWellcomeCentre/amap-python/issues/56

[adamltyson]

I think this can be solved by just adding quotes to the paths sent to niftyreg.

[adamltyson]

This is also an issue if brainreg is installed in a directory with spaces, as the path to niftyreg is used as a command to bash/cmd.

[adamltyson]

Fixed in 649a915

[adamltyson]

Not fully fixed - output files are incorrectly named.